From PC World (and also a ton of other places via press release): "After a first successful season running 802.11n high-speed Wi-Fi throughout its glimmering new ballpark, Nationals Park officials in Washington plan to add more applications for next year, including video game clips that fans at the park can wirelessly pick up on their handhelds. [...] In addition to sending video clips of spectacular game plays to fans at Nationals Park, Zachariah said he hopes to have other types of wireless interactions between fans. Among these is making it possible for fans to send text comments or photos that could be posted on the park's 4,800-square-foot high-definition scoreboard. Plans also include using RFID (radio frequency identification) tags to track cash bags over the Wi-Fi network as they are carried from a concession stand to the safe, Zachariah added. The tags could also be distributed to parents who could attch them to their children, in case they get lost in the ballpark. Plans for next spring also include allowing a voice over Wi-Fi system for stadium staff to use during emergencies when cellular networks may be overtaxed, Zachariah added. Fans could also place food orders over Wi-Fi and have the orders delivered to their seats."

The article says it cost about $280,000 for all the equipment and installation.